email Bulletproof Buttons Padding + Border-Based Buttons

Example

This technique uses a combination of border-based and padding-based buttons, styling the link with both padding and at least a solid 1px border. The background color needs to be applied to the instead of the in this instance because Outlook does recognize horizontal padding on the tag (since it's not a block level tag).

<table width="100%" border="0" cellspacing="0" cellpadding="0">
  <tr>
    <td>
      <table border="0" cellspacing="0" cellpadding="0">
        <tr>
          <td align="center" style="-webkit-border-radius: 3px; -moz-border-radius: 3px; border-radius: 3px;" bgcolor="#0095FF"><a href="https://www.stackoverflow.com" target="_blank" style="font-size: 14px; font-family: sans-serif; color: #ffffff; text-decoration: none; text-decoration: none; -webkit-border-radius: 3px; -moz-border-radius: 3px; border-radius: 3px; padding: 12px 18px; border: 1px solid #0095FF; display: inline-block;">Stack Overflow</a></td>
        </tr>
      </table>
    </td>
  </tr>
</table>

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The drawback of padding+border-based-buttons is that it separates the styling between a <td> and <a> tag, so it can be difficult to maintain. But only one button is used, specific dimensions are not required, and background images can be supported.